CA1045737A - Solid urea-formaldehyde bead formation - Google Patents

Abstract

ABSTRACT

A process of preparing bends of urea-formaldehyde resin in which disperse particles of an aqueous urea-formaldehyde syrup are converted to hard polymer and azeotropically dehydrated. The aqueous syrup must have a solids content of at least 65% by weight and the mol ratio of formaldehyde to urea must be within the range of 1.9 - 2.3 to 1.

Description

This invention relates to a process of preparing a texturing agent and filler comprising beads of urea-formaldehyde resin and to beads so-produced.
Powdered polymer in the form of particles ranging in size from about 50 micron to a few mm diameter have been prepared from bulk polymer such as poly(ethylene), poly ~propylene) and phenol-aldehyde condensates. The use of such materials as fillers or texturing agents in, for example, moulded plastics articles and paints has been proposed. Particles of this type have been made by, for example, milling polymer at temperature below its glass transition temperature, which is a relatively costly process. ~he particles produced by the mechanical reduction of bulk polymer are frequently angular and this can give rise to uneven and hence unacceptable optical effects when used as, for example, texturing agents in paints.
Canadian Patent No. 970,488, filed March 18, 1971, in the name of Dulux Australia Ltd., discloses the preparation of granules of amine-formaldehyde polymer by a dispersion process which converts particles of polymer precursor elements directly into polymeric granules. The granules so-produced are porous.
They are permeated by a net-like web of inter-connected pores . . .
which are capable of imbibing liquids in which the granules are immersed and are referred to as "retiporous" particles. It is :.,, ~' proposed that the granules be used as opacifying and texturing agents in a num~er of media including paints and plastics ., .

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~5~37 ~ t~le have observed -that the use of porous pol~ymer .. .. .
~; particles as mattlng agents in certain products?
~; notably matt and sèmi-gloss paints, can le&d to uneven and variable colour development in the dry paint films due, we believeq to uncontrollable and unpredictible i, imbibing of liquid constituents of the paint by the porous particles~
Je have now discovered that solid polymer be~ds with diameters within the range of 1-100 micron can be produced from aqueous ursa-formaldehyde syrups in the manner hereinunder described and that the beads ~ii so-produced can be used as texturing agents and fillers with certain advalltages, which will become apparent from our disclosures, over the above-mentioned retiporous granules for soIJe specific applicationsO Our process ~, .
involves preparing the beads in the form of an anhydrous slurry, which can be used directly in, for example, non-aqueous paint compositions or which can be dried to produce solid beads in the form of a dry powder.
~he procegs we now disclose involves the dispersion i~ of an aqueous urea~formaldehyde convertible syrup in a hydrocarbon liquid in globules of approximately the ~ ' '.;.'1' .
diameter of the required beads, curing of the convertible syxup to solidt cross-linked polymer and azeotropic stripping of water from the s~stem to gi~e an anhydrous slurry of beads in hydrocarbor, liquid. Optionally, ....
the hydrocarbon liquid can be removed, for example by ~ing under reduced pressure~ to produce a dr~
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: ' 1~5737 powder of ~olid beads~ ~
The general principles of formulatin~ convertible urea-formaldehyde syrups are well-known in the art and the selection of this component for use in our invention demands no more than the exercise of known .
principles of polymer technology. However, we have found that two unusual requirements must be met if ; satisfactory beads are to be made; the mol ratio of formaldehyde to urea used to prepare the convertible ` 10 syrup must be 1.9 ~ 2.~ to 1 and the solids content o~
~` the syrup must be at least 65% by weight. If these :,, requirements are not met, ca~ities or pores will normally form in the beads.
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~lthough the convertible constituents of the syrups we use are essentially urea-formaldehyde reaction ` products~ it is known that minor additions of other carbamides, amino-triazines and compounds of similar cheTnic~l structure may be made to the urea to imbue ~ the final cured resiI with modified mechanical .~ 20 - properties~ Such minor modifications are comprehended in our use of the term urea-formaldehyde convertible syrup.
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~ he convertible syrup is dispersed with mechanical agitation in the form of discrete globules in a non-aq~leous liquid continUous phase in ~hich it is insoluble, in the presence of a stabiliser and thickener~ to produce disperse particles of the order of siæe required in the completed beads. ~he diameter of the disperse , . .

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` ~ 9L5737 ^ globule~ is controlled by kno~vn techniques~ utilisin~
,~- time and rate of agitation and the relative viscosities ' of the continuous and disperse phases to arri^ve at the required disperse globule diameters.
^ 5 ~he non-aqueous liquid in which the conver~ible ," syrup is dispersed must be a non-solvent for and , chemically inert toward the reactive constituentsof the ~'; convertible syrup and the granules. By the reactive , ^;, .
'', constituents of the syrup we mean those precursor i^ 10 elements which, on further condensat,ion, form the ^ . ^- . .
,/'`~ polymer of the granules. In general, this will mean ~,.^. . .
',',,` 'that the non-aqueous liquid is incompatible with the ;,;-- convertible syrup. For example the liquid may be an . ....
' essentially aliphatic hydrocarbon such as heptane, . . ~................ .
'~"'^ 15 hexane or a commercial mixture of hydrocarbons, e~g.
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~,,', petroleum ether and white spirits.^ ~lternatively , .,.,., ~ .
~ the non-aqueous liquid may comprise other liquids, ~or ~:, "-' example aromatic hydrocarbons, e.g. toluene~ xylene ,,~', `and petroleum naphthas. It is not essential that the ,',''' 20 non-aqueous liquid be completely insoluble in the ; convertible syrup provided it does not dissolve the ~,' reactive constituents and cause them to pass into the ~; continuous phase of the dispersion. Furthermore, when ~' there is present in the non-aqueous liquid a proportion ',,',',, 25 of a liquid which has a measurable solubility in :, . .
~he aqueous syrup~ a propor^tion of the soluble liquid ~''' may partition into the aqueous syrup. This is not ~ ~ ", ,l'`^ ' objectionable provided the solids co,ntent of the. . .
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~~ disperse globules of convertible syrup ls not reduced below 65Yo by ~veight. Conversely~ if a proportion of the aqueous liquid partitions into the continuous ; phase, this also is not objectionable provided the convertibility of the syrup is not affected.
; Effective stabilisation of the disperse globules is provided by dissolving in the continuous phase a polymeric amphipathic stabiliser co~rising segments which are soluble in the continuous phase and components, ,.. .
for example hydroxyl groupsg which have a~ affinity for ; the disperse globules. Suitable 2~phipathic stabilisers are, for example~ hydroxyl-containing addition polymers of ethylenically unsaturated monomers, containing 5-20 mol percent of hydroxyl groups. ~or example, a suitable stabiliser for use in an aliphatic non-a~ueous ,....
~ liquid is a copolymer of 2-ethyl hexyl acrylate and (. :.
~ hydroxy propyl methacrylate. If the non-aqueous liquid , ....... .
comprises solle aromatic ring compounds such as toluene and xyler.e, we would replace the 2-ethyl hexyl acrylate with styrene. ~he stabiliser i5 typically used at ; concentrations of the order of 1% by weight of the continuous phase.
We also require that the continuous phase shall be , .. ...
sufficiently viscous to provide an efficient dispersion medium for the convertible aqueous syrup, ~he viscosity is increased by dissolvin~ therein a soluble pol~meric ~; material, the nature of which is not critical and conveniently related to the intended end-use of the beads.
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For example, if the beads are to be used as texturing agents in alkyd resin enamels, it would be satïsfactory . .
to use a similar alkyd resin as the thickening agent, .
thus avoiding the need to remove what migh-t otherwise be a harmful contaminant from the beads after they are converted, before they could be used in the enamel.
It may well be that the stabiliser will itself provide sufficient viscosity in the continuous phase or it may be convenient to add excess stabiliser to ser~e the dual role of thickener. In general, therefore, we find that the amount of thickener used will vary from ., .
;`; zero to 15% by weight of the continuous phase~
: Condensation of the disperse syrup globules to hard polymer is induced by-adding a suitable cataly~t~
for example a mineral acid, e.gO sulphuric acid, to the dispersion. ~he catalyst may be added prior to~
during or after the formation of the lnitial dispersion.
Optionali~ the ~ispelsiGiL may be heatad to ~ccclerate the reaction. Although the choice of catalyst is not : , .
~0 critical, ~e prefer to use sulphuric acid because ; excess catalyst can be readily disposed of by reacting ., it with calcium carbonate. ~he calcium sulphate so-~; formed is normally not an objectionable impurity in -the . . , beads - 25 ~Ne prefer to use a concentration of catalyst which will cause gellation of the dispersed globul~
within about one hour~ a typical concentration bein~
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` 0~3~o by weia~ht of 20% sulphuric acid, based on the ., , , -- -- .

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eig}lt o~ s~rup to be conv~rted. Complete curing of the beads to ~he hard condition usually requires some 24 hours.
` ~he slurry of beads so-produced is then azeotroped~
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that is it is boiled under reflux conditions and ~Jater stripped off from the reflux condensate, the non-aqueous ` ~ condensate being returned to the batch~ Azeotroping is - continued until no further water is being stripped from the batch.
I~ required, the beads can be collcentrated, e.g.
~, by filtration or centrifuging and finally dried, for example by heating under partial vacuum, to provide~dry ~ powdered mass of beads. However when~ ~or example~
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~ the beads are to be used as texturi~g agents in non-, .
~ aqueous paints a it is more usual to a~oid the expense :, - .
of drying by incorporating them directl~ in the paint as a slurry.
he beads may optionally be pigmented to impart opacity and or colour to them or to modify their ;; 20 mechanical properties. ~his is done by dispersing ` ~ pigment in the convertible aqueous syrup be~ore it i~
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~ dispersed in globules. ~he process proceeds otherwise . . .
i as described hereinabove. ~here are no limitation~
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imposed on the selection of pigment other than the predictible one that th~ pigment shall be inert wi~h < respect to the polymerisation reaction. ~t can be i~ ; dispersed in the syrup by the usual techniquesg for , ... .
`` ~xal~ple ~y the use o~ a high-speed stirrer~
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~S737 A particularly use~ul pigmen~ is titanium dioxide, which we have used to produce opaque matting and texturing agents of this type.
This in~ention is illustrated by the following examples in which all parts are given by weight :

EXAM~IE I

Preparation of solid spheroidal polymer granules b~ the condensation of an aqueous syrup of ~ low molecular weight urea-formaldehyde condensate precursor ~ormaldehyde/urea molar ratio 2D2/1)) the aqueous syrup being dispersed as discrete particl~s in a hydrocarbon solution of a stabilizer and a thlck~ner~
The convertible aqueous qyrup was prepared by heating the following mixture to reflux and holdi 15 for 5 minutes.
~ater 20.80 parts ~riethanolamine 0.05 80% paraformaldeh~de ~5083 "
Urea 33~32 "
~he mixture was made acid by the addition of 0.005 parts of formic acid, refluxing resumed for 23~ hours, b 0.31 parts of a 10k by weight aqueous solution of pot~ssi~ hydroxide added and the syrup cooled.
~his syrup had a Gardner-Holdt viscosity of H.
When 1~0 pa~rts o~ the syrup was mixed with 0.8 parts of a molar solution of sulphuric acid the mass gell~d in 70 minutes.

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0~5737 ~ he stabiliser was prepared by the addi-tion polymerisation of the following mixture in 500 parts of refluxing xylene~
Styrene ~23.0 parts Methyl methacrylate84~0 " .
Butyl acrylate 134.0 "
Butyl methacrylate 75.0 Hydroxy propyl acrylate80~0 Acrylic acid 5~0 Ditertiary butyi peroxide ~.0 ~ his stabiliser solution had a Gardner Holdt viscosity of U.
~ he th1ckener used in this example was a 40% by ~eight solution of poly(methyl methacrylate) in tolueneg the pol~mer ha~ing a relative viscosity of 1~170.
Relative viscosity i5 defined as the ratio of the absolutely viscosity of a solution of a polymer in a solvent to the absolute viscosity of the pure solvent and is an art-xecognised method.of specifying a - 20 particular molecular weight range (seel fox example, ~ :
"~extbook of Polymer Science" (2nd Editio~) by Billmèyer (Wil~y-Interscience)~ page 84).
Condensation and granulation of th~ aqueous syrup was carried out ~y rapidly dispersing 200 par~s of the above Sylup mix~d with 1.6 parts of molar sulphuric . acid into a mixture of 5.0 part~ of sta~iliser~
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50.0 parts of thickener and 50 parts of ~ylene.
~he beads so-.pr~pared showed no internal structure and had an ~verage diameter of ap~roximately 20 micron.
150 parts o~ toluene were then added and the bead slurry allowed to stand to allow the cure to proceed to completion.
Water was then removed from the system by a~eotropic distillation to give an anhydrous slurry o~
solid urea-formaldehyde beadsO

EX~MP~E II

~ he procedure of example I was repeated except that the aqueous syrup was prepared from formaldehyde and urea in the ratio of 1.7 to 1~ ~his gave a cloud~
~yrup which contained insoluble particles and produoed unsatisfactory beads which were cloudy and of non-3ph~r~cql sh~pP, , ' ' ~ EXAM~IE III
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.~he p~ocedure o~ examE,le I was repeated but 55 parts of water were added to the aqueous syrup to reduce the ~olids to 55% by weight. The beads produced from this syrup w~re cellular and porou~ and when dried co~lld be observed under a microscope to ; ~mbibe liquid when immersed in an alkyd resi~l sol~on.
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~XAMP~E IV

Preparation of solid pigmented spheroidal polymer granules, ~ he preparation of these pigmented granules was 5 carried out using the methods 9 materials and quan~ties of Example I except for the replacement of the condensation and granulation stage of that example by the following stageO
100 parts of rutile titanium dioxide pigment were dispersed in 200 pa~ts of the convertible aqueous syrùp of Example I by high speed mixing. 2.5 parts of 2D5 molar sulphuric acid were then mixed into this dispersion, and the dispe~sion was rapidly dispersed into a mixture of 5~0 parts of stabili~er, 50.0 parts of thickener and 50 parts of xylene. ~he remainder of the preparation was identical to that o~ Example I~
~ he beads prepared by the above method contai~ied pigment which was uniformly distributed throughout themc ~hey had. an a~erage diameter of approximately 20 micron and showed no internal structure.

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Claims (2)

The embodiments of the invention in which a particular property or privilege is claimed are defined as follows:

1. A process of preparing beads of urea- formaldehyde resin in which an aqueous urea-formaldehyde convertible syrup which has a solids content of at least 65% by weight and a mol ratio of formaldehyde to urea of 1.9 - 2.3 to 1 is dispersed in the form of globules in a hydrocarbon liquid in the presence of a polymeric amphipathic stabiliser for the dispersion and from 0 to 15% by weight of the continuous phase of a dissolved polymeric thickener therefor, converting the disperse syrup globules to hard polymer by adding a catalyst for the curing reaction and then azeotropically stripping water from the system to give an anhydrous slurry of beads with diameters within the range of 1-100 microns in hydrocarbon liquid.

2. A process according to Claim 1 wherein the catalyst for the curing reaction is sulphuric acid.